In a two-cylinder type rotary compressor, a refrigerant path hole through which a high-temperature compressed refrigerant that is compressed in a lower cylinder and is discharged from a lower discharge hole flows toward an upper end plate cover chamber (upper muffler chamber) from a lower end plate cover chamber (lower muffler chamber), is disposed at a position separated from an inlet chamber side of the lower cylinder and an upper cylinder. Accordingly, a technology which suppresses heating of a suctioned refrigerant on the inlet chamber side of the lower cylinder and the upper cylinder due to the compressed refrigerant, and in which compressor efficiency is improved, is known.
In addition, in the two-cylinder type rotary compressor, a technology which suppresses heating of the lower end plate and heating of the suctioned refrigerant on the inside of the inlet chamber of the lower cylinder due to the high-temperature compressed refrigerant that is compressed in the lower cylinder and is discharged from the lower discharge hole, and in which compressor efficiency is improved, is known.
In a rotary compressor described in JP-A-2014-145318, as a lower end plate cover (lower muffler cover) inflates, capacity of a lower end plate cover chamber formed between a lower end plate and the lower end plate cover becomes greater. Therefore, an amount of a refrigerant which is compressed in an upper cylinder, is discharged from an upper discharge hole, flows backward through a refrigerant path hole, and flows into a lower muffler chamber, is large.
In a rotary compressor described in International Publication No. 2013/094114, a refrigerant path hole is disposed on a side opposite to a lower discharge valve accommodation portion with respect to a lower discharge hole provided in a lower end plate, a refrigerant discharged from the lower discharge hole flows to the refrigerant path hole through the lower discharge valve accommodation portion, and accordingly, it is necessary to deepen the lower discharge valve accommodation portion. Therefore, capacity of a lower end plate cover chamber (refrigerant discharge space) increases, and an amount of the refrigerant which is compressed in an upper cylinder, is discharged from the upper discharge hole, flows backward through the refrigerant path hole, and flows into a lower muffler chamber, is large.
Hereinafter, the above-described backflow phenomenon of the refrigerant will be described. In a two-cylinder type rotary compressor, in order to reduce a fluctuation in torque per one rotation of a rotation shaft to be as small as possible, in general, a process of suctioning, compressing, and discharging is performed with phases different by 180° in two cylinders. Excluding a special operating condition, such as a condition at the time when staring an operation, in an operation of an air conditioner at a general outdoor temperature and an indoor temperature, the discharge process of one cylinder is approximately ⅓ of one rotation of the rotation shaft. Therefore, ⅓ of one rotation is a discharge process (process in which a discharge valve is open) of one cylinder, and the other ⅓ of the rotation is a process of discharging of the other cylinder, and remaining ⅓ of the rotation is a process in which both of the discharge valves of two cylinders are closed.
Here, when both of the discharge valves of two cylinders are closed, and the refrigerant discharged from the compression chamber does not flow, pressures of an upper end plate cover chamber and a lower end plate cover chamber become the same pressure on the inside of a compressor housing on the outside of the upper end plate cover chamber. In the discharge process of one cylinder, among high-pressure compressed regions, the pressure of the compression chamber which is on the most upstream side of the flow of the refrigerant is the highest, and then, the pressures of the upper end plate cover chamber and the inside of the compressor housing on the outside of the upper end plate cover chamber, are high in order. Therefore, immediately after the discharge valve of the upper cylinder is open, the pressure of the upper end plate cover chamber becomes higher than the pressure of the inside of the compressor housing on the outside of the upper end plate cover chamber, or the lower end plate cover chamber. Accordingly, in the next moment, a flow of the refrigerant to the lower muffler chamber which flows backward on the inside of the compressor housing that is on the outside of the upper end plate cover chamber and the refrigerant path hole, from the upper end plate cover chamber, is generated.
The original flow of the refrigerant is a flow to the inside of the compressor housing on the outside of the upper end plate cover chamber, from the upper end plate cover chamber. However, the refrigerant which flows to the lower end plate cover chamber from the upper end plate cover chamber flows to the inside of the compressor housing on the outside of the upper end plate cover chamber through the refrigerant path hole and the upper end plate cover chamber again after finishing the discharge process of the upper cylinder, and originally, the flow is an unnecessary flow. Therefore, there is a problem that energy loss is generated and the efficiency of the rotary compressor deteriorates.
In addition, in the rotary compressor described in International Publication No. 2013/094114, heating of the lower end plate which covers a lower surface of the lower cylinder due to the refrigerant compressed in the lower cylinder, is suppressed. However, in the rotary compressor, in particular, in a state where external air is stopped for a long period of time in a low-temperature atmosphere, there is also a case where the liquefied refrigerant (liquid refrigerant) remains on the inside of the compressor housing. Since density of the liquid refrigerant at a low temperature is higher than density of lubricant oil, the liquid refrigerant remains in the lowest portion on the inside of the compressor housing. In this state, when the rotary compressor is started to be operated, the liquid refrigerant is suctioned up by an oil feeding impeller from a lower end of the rotation shaft. When the liquid refrigerant is suctioned up, since viscosity of the liquid refrigerant is lower compared to viscosity of the lubricant oil, there is a concern that defective lubrication occurs and a sliding portion of a compressing unit is damaged.
Therefore, when starting to operate the rotary compressor, it is necessary to quickly heat and gasify the liquid refrigerant. However, similar to the rotary compressor described in International Publication No. 2013/094114, in a case where the heating of the lower end plate is suppressed, gasification caused by the heating of the liquid refrigerant that remains in the lower portion of the compressor housing is suppressed, and there is a problem that damage is generated due to defective lubrication of the compressing unit as the oil feeding impeller suctions up the liquid refrigerant.
In addition, in the rotary compressor, a part of the lubricant oil on the inside of the compressor housing is entangled in the refrigerant, and is discharged to the outside of the compressor housing. The lubricant oil discharged to the outside of the compressor housing circulates a refrigerant circuit (refrigeration cycle) of the air conditioner, and is suctioned to the lower cylinder and the upper cylinder together with the suctioned refrigerant. The lubricant oil suctioned to the lower cylinder is discharged to the lower end plate cover chamber from the lower discharge hole together with the refrigerant. The lubricant oil discharged to the lower end plate cover chamber remains in the lower end plate cover chamber, and when the lower discharge hole is immersed in the lubricant oil, there is a problem that discharge resistance of the refrigerant is generated, efficiency deteriorates, and noise is generated. This problem is likely to be generated as the capacity of the lower end plate cover chamber decreases.